Fuel injection sydtem

ABSTRACT

A fuel injection system capable of improving the degree of atomization and the combustibility of a fuel, including a fuel swirler, a valve seat having a fuel injection port, an annular fuel swirl chamber formed between the fuel swirler and a valve seat and communicating with plural swirl grooves and a fuel injection port, and a valve body adapted to be moved forward and backward in the interior of the fuel swirler in the axial direction thereof and thereby disengaged from and engaged with the valve seat to open and close a communication passage between the fuel swirl chamber and fuel injection port. Let S 1,  S 2  and S 3  equal a minimum cross-sectional area of an opening between the valve body and valve seat in the condition in which the communication passage is fully opened, an area of a cross section of the fuel injection port which is perpendicular to the axis thereof, and an average cross-sectional area of a fuel flow in the fuel injection port, respectively. A stroke amount of the valve body is set so that a minimum cross-sectional area of the mentioned opening satisfies the following expression: 
     
       S 
       3&lt; 
       S 
       1&lt; 
       S 
       2

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a fuel injection system adapted toapply swirling energy to a fuel and supply the resultant fuel to acombustion chamber of an internal combustion engine, such as anautomobile engine.

[0003] 2. Description of the Related Art

[0004] Fuel injection systems utilizing the techniques for providing afuel injection port-carrying valve seat in an outlet of a cylindricalvalve casing having a valve body, such as a needle valve and a ballvalve therein; turning by a swirler a fuel supplied from the outside;and supplying the resultant fuel to the fuel injection port haveheretofore been known from Japanese Patent Laid-Open Nos. 47208/1998 and205408/1998. According to these techniques, a communication passagebetween the fuel swirler and fuel injection port is opened and closed bydisengaging and engaging a part of a free end portion of the valve bodyand a part of the valve seat from and with each other. Let S1 and S2equal a minimum cross-sectional area of a clearance between the valvebody and valve seat in the condition in which this communication passageis fully opened, and an area of the cross section of the fuel injectionport which is perpendicular to the axis thereof, respectively. A flowrate of the fuel then becomes higher in proportion to S1 and S2.

[0005] When the minimum cross-sectional area S1 is larger than thecross-sectional area S2 of the fuel injection port, a fuel having asmall amount of swirling energy is injected in large quantities from thefuel injection port in an initial period of a fuel injection operation.Since this fuel has a small amount of swirling energy, the diffusivityof fuel spray and the atomization of the fuel are insufficient, so thatthe combustibility of the fuel in a cylinder of an engine isdeteriorated. Conversely, when the minimum opening area S1 is smallerthan the cross-sectional area S2, this problem is solved or lightened.However, when S1 is excessively smaller than S2, a flow resistance ofthe fuel in the communication passage is high, and this causes theswirling energy applied to the fuel by the fuel swirler to bealleviated, a scatter of an angle of spray to increase or thediffusivity of fuel spray and the atomization of the fuel to becomeinsufficient, and thereby the combustibility of the fuel in a cylinderof the engine to be deteriorated.

[0006] The fuel having swirling energy flows through the fuel injectionport not over the whole of its cross section S2 but mainly over theportion of a cross section thereof which is near an inner surface of thefuel injection port, so that a void occurs in an inner portion of thefuel injection port. Japanese Patent Laid-Open No. 47208/1998 disclosesthe techniques for setting S2 larger than S1 for the purpose ofstabilizing a flow of the swirling fuel with the void retained but thispublication does not refer to the above-mentioned problems occurringwhen S1 is excessively smaller than S2. On the other hand, JapanesePatent Laid-Open No. 205408/1998 discloses in contrast with JapanesePatent Laid-Open No. 47208/1998 the techniques for setting S2 smallerthan S1.

SUMMARY OF THE INVENTION

[0007] The present invention has been made in view of theabove-mentioned various problems in this technical field and the presentcondition of the related art, and provides a fuel injection systemcapable of holding down a decrease in the swirling energy of the fueland improving the degree of atomization and combustibility of the fuel.

[0008] The fuel injection system according to the present invention is(1) a fuel injection system including a cylindrical fuel swirler havingplural swirl grooves, a valve seat engaged with a swirl groove-carryingsurface of the fuel swirler and having a fuel injection port, an annularfuel swirl chamber formed between the fuel swirler and valve seat andcommunicating with the swirl grooves and fuel injection port, and avalve body adapted to be moved forward and backward in a cylindricalhole of the fuel swirler in the axial direction thereof and therebyengaged with and disengaged from the valve seat to cause a communicationpassage between the fuel swirl chamber and fuel injection port to beclosed and opened, wherein a minimum cross-sectional area S1 of aclearance between the valve body and valve seat in the condition inwhich the communication port is fully opened being smaller than an areaS2 of the cross section of the fuel injection port which isperpendicular to the axis thereof, and larger than an average area S3 ofthe cross section of the fuel injection port which is perpendicular tothe direction in which a fuel flow advances.

[0009] (2) A fuel injection system according to (1) above, in which thefuel swirl chamber is formed so as to be surrounded by walls of the fuelswirler, valve body and valve seat.

[0010] (3) A fuel injection system according to (1) above, in which thefuel swirl chamber is formed to a circular annular shape, the swirlgrooves extending in a tangential direction of the fuel swirl chamber.

[0011] (4) A fuel injection system according to (1) above, in whichsurfaces of the fuel swirler and valve seat at which these parts contacteach other are inclined with respect to the axes thereof.

[0012] (5) A fuel injection system according to (4) above, in which anangle of inclination of the mentioned surfaces with respect to thementioned axes is not smaller than 45° and smaller than 90°

[0013] (6) A fuel injection system according to (1) or (4), in which theaverage cross-sectional area S3 is determined by using the followingequation:

S3=(π/4){De ² −Q ² sin² ΘDi ²ρ/(2gPA ²)}

[0014] wherein De: an inner diameter (m) of the fuel injection port,

[0015] Q: a static flow rate (m³/s) of a fuel supplied to the fuelswirler,

[0016] A: a total cross-sectional area (m²) of the swirl grooves,

[0017] Di: a length (m) two times as large as an offset amount of thecenter line of the swirl grooves with respect to the center of the fuelswirl chamber,

[0018] Θ: an angle (°) of surfaces of the valve seat and fuel swirler atwhich these parts contact each other with respect to the axes thereof,

[0019] g: gravitational acceleration (m/s²)

[0020] P: pressure (kgf/m²) of the fuel supplied to the fuel swirler,and

[0021] ρ: density (kg/m³) of the fuel.

[0022] (7) A fuel injection system according to (1) above, in which theswirl grooves have a non-squarecross-sectional shape, the volume perunit length of each of the swirl grooves of groove bottoms or theportions of the grooves which are in the vicinity of the groove bottomsbeing smaller than that per unit length of each of the grooves of upperportions of the grooves.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Preferred embodiments of the present invention will be describedin detail with reference to the following figures, wherein:

[0024]FIG. 1 is a sectional view of a mode 1 of embodiment of the fuelinjection system according to the present invention;

[0025]FIG. 2 is an enlarged sectional view of a fuel swirler and aportion in the vicinity thereof in the mode 1 of embodiment;

[0026]FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

[0027]FIG. 4 is a sectional view taken along the line IV-IV in FIG. 2;

[0028]FIG. 5 is a partial enlarged sectional view of a valve seat in themode 1 of embodiment of the present invention;

[0029]FIG. 6 is an enlarged sectional view of a fuel swirler in a mode 2of embodiment of the present invention;

[0030]FIG. 7 is a partial enlarged plan in section of a valve seat-sidesurface of a fuel swirler in a mode 3 of embodiment of the presentinvention;

[0031]FIG. 8 is an enlarged sectional view taken along the lineVIII-VIII in FIG. 7;

[0032]FIG. 9 is an enlarged sectional view of a fuel swirler and aportion in the vicinity thereof in a mode 4 of embodiment of the presentinvention; and

[0033]FIG. 10 is a sectional view taken along the line X-X in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Mode 1 of Embodiment

[0035] FIGS. 1-5 are all such drawings that illustrate the mode 1 ofembodiment of the present invention, wherein FIG. 1 is a sectional viewof a fuel injection system, FIG. 2 an enlarged sectional view of a fuelswirler and a portion in the vicinity thereof, FIG. 3 a sectional viewtaken along the line III-III in FIG. 2, FIG. 4 a sectional view takenalong the line IV-IV in FIG. 2, and FIG. 5 a partial enlarged sectionalview of a valve seat. FIGS. 3 and 4 show in plan a valve seat-sidesurface and a fuel receiving-side surface respectively of the fuelswirler.

[0036] Referring to FIGS. 1-5, a reference numeral 1 denotes a fuelinjection system, 2 a housing of the fuel injection system 1, 3 a fuelinjection valve, 4 a fuel supply pipe, 5 a cylinder head of an engine, 6a valve operating unit having an electromagnetic coil 61 and some otherparts and adapted to operate a needle valve 7, an example of a valvebody. A free end portion of the fuel injection system 1 is inserted andfixed in a fuel injection system inserting hole 51 of the cylinder head5 of the engine. The fuel injection valve 3 has a structure formed byassembling parts including a valve holder 31, the needle valve 7, fuelswirler 8, and valve seat 9 having a fuel injection port 91. The fuelswirler 8 has the functions of applying swirling energy to the fuelsupplied from the fuel supply pipe 4, and supplying the resultant fuelto the fuel injection port 91 of the valve seat 9. A reference numeral83 denotes a cylindrical hole of the fuel swirler 8, and a free endportion of the needle valve 7 is inserted through the cylindrical hole83, a free end of the needle valve reaching an inlet of the fuelinjection port 91.

[0037] As is understood from FIGS. 3 and 4, an outer circumferentialwall of the fuel swirler 8 has a hexagonal shape, so that six clearances84 one side of each of which is shaped like a surface of a convex lensoccurs between an inner surface of the cylindrical valve holder 31 andan outer circumferential surface of the fuel swirler 8. These clearances84 function as fuel passages. A valve seat-side surface 81 of the fuelswirler 8 is provided therein with six cross-sectionally square swirlgrooves 85 extending from open ends of the six clearances 84 toward acylindrical hole 83 of the fuel swirler 8. Between the fuel swirler 8and valve seat 9, six swirl passages 87 (refer to FIG. 2) formed by theswirl grooves 85 and an outer surface of the valve seat 9 exist. At anopen end of the cylindrical hole 83 of the fuel swirler 8, an annulargroove 88 concentric with the cylindrical hole 83 is provided, and thisannular groove 88, outer surface of the valve seat 9 and a side surfaceof the needle valve 7 form an annular fuel swirl chamber 89 (refer toFIG. 2). As shown in FIG. 3, the six swirl passages 87 extend in atangential direction of the fuel swirl chamber 89 to communicate withthe fuel swirl chamber 89, which communicates with the fuel injectionport 91.

[0038] When a fuel supplied from the fuel supply pipe 4 reaches the fuelreceiving-side surface 82 of the fuel swirler 8, it flows into the sixclearances 84 separately, and reaches the valve seat-side surface 81 ofthe fuel swirler 8. While the fuel then flows through the swirl passages87, swirling energy is applied thereto, and the resultant fuel reachesthe fuel swirl chamber 89, the fuel being finally injected from the fuelinjection port 91 of the valve seat 9. During this time, the needlevalve 7 is moved forward and backward in the axial direction thereof inthe cylindrical hole 83 of the fuel swirler 8 and thereby engaged withand disengaged from the valve seat 9 to cause a communication passagebetween the fuel swirl chamber 89 and fuel injection port 91 to beclosed and opened.

[0039] A mechanism for applying swirling energy to the fuel will now bedescribed. As stated before, the length of the swirl passages 87 is setcomparatively large with respect to a cross-sectional area thereof, and,to be more exact, a ratio obtained by dividing the length of thesepassages by an inner diameter thereof is set to not smaller than two.Therefore, as stated before, the velocity of flow distribution of thefuel flowing at outlets of the swirl passages 87 is substantially madeuniform. In this case, the inner diameter of the swirl passages 87 shallbe set equal to that of a cross-sectionally circular passage thecross-sectional area of which is equal to that of the swirl passages 87.A velocity of flow V₁ of the fuel flowing out from the swirl passages 87is expressed by the following equation (1):

V ₁ =Q/A  (1)

[0040] wherein Q represents a static flow rate (m³/s) of the fuelsupplied to the fuel swirler 8, and A total cross-sectional area (m²) ofthe swirl passages 87. In the embodiment of FIG. 3, A represents the sumof the cross-sectional areas of the six swirl passages 87.

[0041] The fuel flowing out from the outlets of the swirl passages 87 ismerged together in the fuel swirl chamber 89, and the resultant fuelmakes a swirling movement. The vorticity El of a swirl flow occurring atthis time is expressed by the following equation (2):

E ₁ =V ₁ Di  (2)

[0042] wherein Di represents a length (m) two times as large as anoffset amount (a distance between the center line of each swirl passage87 and a line passing the center of the fuel swirl chamber 89 andparallel to the center line of the swirl passage 87).

[0043] The fuel turned into a swirl flow in the fuel swirl chamber 89enters the fuel injection port 91 through a clearance between the needlevalve 7 and valve seat 9, and injected to the outside of the fuelinjection port 91 as the fuel generates a swirling movement. Referringto FIG. 5, dotted portions F denote a flow of the fuel on the front andrear sides of the fuel injection port 91. A reference numeral 92 denotesa minimum opening between the needle valve 7 and valve seat 9 in thecondition in which the needle valve 7 is fully opened, and a referenceletter θ an angle of the valve seat 9.

[0044] As mentioned previously, the fuel having swirling energy flowsthrough the fuel injection port 91 not over the whole of thecross-sectional area S2 thereof but mainly close to the inner surface ofthe fuel injection port 91, so that a void occurs in an inner portion ofthe same port 91. Thus, a fuel flow F in the fuel injection port 91 hasa doughnut-shaped cross section, and an average cross-sectional area ofthis fuel flow F which is perpendicular to the direction in which thefuel flow F advances shall be represented by S3. Let S1 equal across-sectional area (minimum cross-sectional area) of the minimumopening 92 in the condition in which the needle valve 7 is fully opened.The minimum cross-sectional area S1 of the minimum opening is set sothat the following expression (3) is established.

S3<S1<S2  (3)

[0045] Setting the minimum cross-sectional area S1 of the minimumopening smaller than the cross-sectional area S2 of the fuel injectionport 91 can prevent a fuel having a small amount of fuel swirling energyfrom being injected in large quantities from the fuel injection port 91in an initial period of an injection operation. Setting the minimumcross-sectional area S1 of the minimum opening larger than the averagecross-sectional area S3 of the fuel flow F holds down the attenuation ofthe swirling energy applied by the fuel swirler 8 to the fuel. Thus, theprinciple of a free vortex that the vorticity of the fuel is maintainedin the communication passage extending from the fuel swirl chamber 89 tothe fuel injection port 91 is established. As a result, the fuel isinjected from the fuel injection port 91 to the out side with sufficientswirling energy retained. During this time, the fuel is diffusedexcellently, and the atomization thereof much progresses, so that theabove-mentioned problems to be solved by the present invention are dealtwith successfully.

[0046] The cross-sectional area S2 of the fuel injection port 91 can bedetermined by actually measuring the inner diameter of the fuelinjection port 91. When the detailed construction of the fuel injectionsystem and the operating conditions therefor are determined, the minimumcross-sectional area Si and average cross-sectional area S3 of the fuelflow F become substantially constant, and, accordingly, thesecross-sectional areas S1, S3 can be actually measured or may becalculated by a method which will be described later. Although theminimum cross-sectional area S1 depends upon a distance between theneedle valve 7 and valve seat 9 in the condition in which the minimumopening 92 is fully opened, it can be set to a desired level byregulating an axial stroke amount of the needle valve 7.

[0047] The minimum cross-sectional area S1 can be calculated as an areaof an inclined surface of a frustum obtained when a segment Y (refer toFIG. 5) on a normal between the needle valve 7 and valve seat 9 in theminimum opening 92 with the needle valve 7 in a fully opened state isturned around the axis of the fuel injection system; i.e., in accordancewith the following equation (4):

S1=π[ (R+Y)² −R ²] cos (θ/2)  (4)

[0048] wherein R represents the length (refer to Fig. 5) of an inclinedsurface of a removed pointed head portion of the frustum, and θ an angleof the valve seat.

[0049] A method of calculating the average cross-sectional area S3 ofthe fuel flow F will now be described. Since the vorticity is constantaccording to the principle of a free vortex, the following equations (5)and (6) are established on the basis of the above equation (2):

V ₁ Di=V ₂ Dc  (5)

S3=π(De ² −Dc ²)/4  (6)

[0050] wherein V₂ represents a velocity of flow of the fuel in the fuelinjection port 91, and Dc a diameter of a void of fuel in the fuelinjection port 91. The V₂ is set so that a fuel pressure P/ρ, thepotential energy supplied to an upstream side of the fuel swirler 8 issubstantially converted into V₂ ²/(2g), kinetic energy with a fluid lossin the fuel injection port 91 kept low. Therefore, concerning V₂, thefollowing equation (7) is established on the basis of the Bernoulli'stheorem, and the following equation (8) on the basis of the equation(7).

V ₂ ²/(2 g)=P/ρ  (7)

V ₂={square root}(2 gP/ρ)  (8)

[0051] wherein g represents gravitational acceleration (m/S²), P apressure of the fuel supplied to the fuel swirler 8, and ρ the density(kg/m³). Therefore, the following equation (9) is established on thebasis of the above equations (1), ( 6) and (8).

S3=(π/4){De ² −Q ² sin² ΘDi ²ρ/(2gPA ²)}  (9)

[0052] wherein Θ represents an angle (°) of the surfaces of the valveseat 9 and fuel swirler 8 at which these parts contact each other, withrespect to the axes of the same parts, and this angle in the embodimentof FIG. 2 is 90°.

[0053] Mode 2 of Embodiment

[0054]FIG. 6 is a sectional view of a fuel swirler and a portion in thevicinity thereof in a mode 2 of embodiment of the present invention, inwhich a reference numeral 89 denotes a fuel swirl chamber. In FIG. 6 andthe drawings following the same, the parts identical with those shown inFIGS. 1-5 are designated by the same reference numerals.

[0055] In the previously described mode 1 of embodiment, the fuel swirlchamber 89 is formed by the outer surfaces of the annular groove 88provided in a fuel swirler 8 and valve seat 9 and the side surface ofthe needle valve 7. On the other hand, a fuel swirl chamber 89 in themode 2 of embodiment is defined by the side surfaces of the fuel swirler8 and a needle valve 7 and an outer surface of a valve seat 9, and has atriangular cross section. Thus, the mode 2 of embodiment is differentfrom the mode 1 of embodiment in the method of forming the fuel swirlchamber 89. The mode 2 of embodiment is advantageous in that theformation of the annular groove 88 communicating with the fuel swirlerin the mode 1 of embodiment can be omitted to cause the cost ofmanufacturing the fuel swirler 8 to be reduced.

[0056] Mode 3 of Embodiment

[0057] FIGS. 7-8 are drawings both of which illustrate a mode 3 ofembodiment of the present invention. FIG. 7 is a cross-sectional viewcorresponding to FIG. 3. FIG. 7 shows a valve seat-side surface of afuel swirler in plan, and FIG. 8 is an enlarged cross-sectional viewtaken along the line VIII-VIII in Fig.7. Referring to Figs.7-8, areference numeral 85 denotes swirl grooves provided in a fuel swirler 8.Each of the swirl grooves 85 in the previously-described mode 1 ofembodiment has a square cross-sectional shape but each of the swirlgrooves 85 in the mode 3 of embodiment has a V-shaped cross-sectionalshape as shown in FIG. 8. The fuel swirler 8 is produced by using amold, such as a mold of a sintered body. In order to obtain the swirlgrooves 85 having a square cross-sectional shape, it is necessary tosecure the strength of groove-forming portions of the mold. However, inorder to obtain swirl grooves 85 having aV-shaped cross-sectional shape,the degree of securing the strength of the groove-forming portions ofthe mold may be at a lower level. In the case of the swirl grooves 85having a square cross-sectional shape, the velocity of flow of the fuelflowing in the vicinity of bottom surfaces thereof becomes low ascompared with that of the fuel flowing in the central portions thereof.On the other hand, in the case of the swirl grooves 85 having a V-shapedcross section, the volume of the groove bottoms is smaller, and apercentage of the fuel flowing at a low velocity of flow is smaller, sothat an average velocity of flow of the fuel is higher than that of thefuel flowing in the cross-sectionally square swirl grooves. Thus, a fuelswirling energy application efficiency of the fuel swirler 8 is improvedadvantageously.

[0058] Even the swirl grooves having a non-square cross-sectional shapenot limited to swirl grooves having a V-shaped cross section, in whichthe volume per unit length of each groove of the bottom portions or theportions thereof which are in the vicinity of the bottom portions issmaller than that of the upper portions of the same grooves, forexample, cross-sectionally U-shaped swirl grooves, semicircular swirlgrooves or some other shape of swirl grooves which have reduced volumeof groove bottoms have advantages identical with those of thecross-sectionally V-shaped swirl grooves.

[0059] Mode 4 of Embodiment

[0060] FIGS. 9-10 are drawings all of which illustrate a mode 4 ofembodiment of the present invention. FIG. 9 is an enlarged sectionalview of a fuel swirler and a portion in the vicinity thereof, and FIG.10 a sectional view taken along the line X-X in FIG. 9. FIG. 10 alsoshows in plan a valve seat-side surface of the fuel swirler. The mode 4of embodiment is different from the mode 1 of embodiment only in thatsurfaces of a fuel swirler 8 and a valve seat 9 at which these partscontact each other are inclined at an angle Θ with respect to the axesthereof. In this case, an average cross-sectional area S3 can also bedetermined in accordance with the above-mentioned equation (9). In themode 1 of embodiment, the angle Θ is 90°, and the member sin Θ² 1.However, in the mode 4 of embodiment, this member is a value smallerthan 1.

[0061] When the surfaces of the fuel swirler 8 and valve seat 9 at whichthese parts contact each other are inclined with respect to the axesthereof, swirl grooves 85, and, therefore, swirl passages 87 as well areinclined. Consequently, the variations of angle of a fuel passageextending from the swirl passages 87 to a clearance (communicationpassage) between a needle valve 7 and a valve seat 9 via a fuel swirlchamber 89 becomes gentler than that in the mode 1 of embodiment.Therefore, a flow resistance of a fuel becomes lower, so that a fuelflow is further stabilized. Since an efficiency of applying swirlingenergy to the fuel by the fuel swirler 8 decreases as the angle Θdecreases from 90°, the angle Θ is set to a level in the range of45°-90°, and preferably to a level between not lower than 45° and lowerthan 90° when much importance is attached to the stabilization of a fuelflow.

[0062] As described above, the fuel injection system according to thepresent invention is (1) a fuel injection system including a cylindricalfuel swirler having plural swirl grooves, a valve seat engaged with aswirl groove-carrying surface of the fuel swirler and having a fuelinjection port, an annular fuel swirl chamber formed between the fuelswirler and valve seat and communicating with the swirl grooves and fuelinjection port, and a valve body adapted to be moved forward andbackward in a cylindrical hole of the fuel swirler in the axialdirection thereof and thereby engaged with and disengaged from the valveseat to cause a communication passage between the fuel swirl chamber andfuel injection port to be closed and opened, a minimum cross-sectionalarea S1 of a clearance between the valve body and valve seat with thecommunication port fully opened being smaller than an area S2 of thecross section of the fuel injection port which is perpendicular to theaxis thereof, and larger than an average area S3 of the cross section ofthe fuel injection port which is perpendicular to the direction in whicha fuel flow advances. Therefore, a principle of a free vortex by which avorticity of the fuel in the communication passage extending from thefuel swirl chamber to the fuel injection port is maintained isestablished. As a result, the fuel is injected from the fuel injectionport to the outside with the fuel retaining sufficient fuel swirlingenergy. During this time, the atomization of the fuel progresses, andthe problems to be solved by the present invention are dealt withsuccessfully. Moreover, the responsibility of a valve body becomeshigher as compared with that of the valve body, which is set to anunnecessarily large stroke, of the related art fuel injection systemdisclosed in Japanese Patent Laid-Open No. 205408/1998 referred toabove. This enables a high responsibility which, especially, a fuelinjection system for inside-cylinder injection demands to be attained.

[0063] In (2) a fuel injection system, the fuel swirl chamber is formedso as to be surrounded by the walls of the fuel swirler, valve body andvalve seat, so that it is not necessary to provide an annular groove forforming a fuel swirl chamber in the fuel swirler. Therefore,the cost ofmanufacturing the fuel swirler thereby decreases to advantage.

[0064] According to the present invention, the shape of the fuel swirlchamber may be circular, elliptic, polygonal or of some other shape aslong as it extends annularly, and the direction in which the swirlgrooves extend with respect to the fuel swirl chamber is not speciallylimited. In the (3) fuel injection system, the fuel swirl chamber isformed to a circularly annular shape, and the swirl grooves are formedso as to extend in the tangential direction of the fuel swirl chamber.This enables the flow resistance of the fuel to be maintained at aminimum level, and the swirling energy applying function of the fuelswirler to be utilized maximally.

[0065] In (44) fuel injection system, the surfaces of the fuel swirlerand valve seat at which these parts contact each other are inclined withrespect to the axes thereof. When the angle of inclination of thesesurfaces is not smaller than 45° and smaller than 90° as in (5) fuelinjection system, the swirl passages are also inclined, so thatvariation of the angle of the fuel flow passage extending from the swirlpassages to the communication passage between the needle valve and valveseat via the fuel swirl chamber becomes gentle. This causes the flowresistance of the fuel flow to become low, and the fuel flow to be morestabilized effectively.

[0066] When the average cross-sectional area S3 defined in (6) fuelinjection system can be determined in accordance with the above equation(9), the minimum cross-sectional area S1 of the opening between thevalve body and valve seat with the communication passage fully opened,and, furthermore, an optimum stroke amount of the valve body can bedetermined by making calculations on the basis of the detailedconstruction of the fuel injection system according to the presentinvention and various conditions for the supply fuel.

[0067] Moreover, when the swirl grooves of (7) fuel injection systemhave a non-square cross-sectional shape with the volume per unit lengthof each of the grooves of the groove bottoms and the portions thereofwhich are in the vicinity of the groove bottoms smaller than that of theupper portions of the grooves, the manufacturing of the fuel swirler byusing a mold of a sintered body is done easily. Since the percentage ofthe fuel the velocity of flow of which becomes low due to the smallvolume of the groove bottoms is small, the average velocity of flow ofthe fuel is higher than that of the fuel flowing in thecross-sectionally square grooves. Accordingly, the fuel swirling energyapplication efficiency of the fuel swirler is improved.

What is claimed is:
 1. A fuel injection system comprising a cylindricalfuel swirler having plural swirl grooves, a valve seat engaged with aswirl groove-carrying surface of the fuel swirler and having a fuelinjection port, an annular fuel swirl chamber formed between the fuelswirler and valve seat and communicating with the swirl grooves and fuelinjection port, and a valve body adapted to be moved forward andbackward in a cylindrical hole of the fuel swirler in the axialdirection thereof and thereby engaged with and disengaged from the valveseat to cause a communication passage between the fuel swirl chamber andfuel injection port to be closed and opened, wherein a minimumcross-sectional area S1 of a clearance between the valve body and valveseat with the communication port fully opened being smaller than an areaS2 of the cross section of the fuel injection port which isperpendicular to the axis thereof, and larger than an average area S3 ofthe cross section of the fuel injection port which is perpendicular tothe direction in which a fuel flow advances.
 2. A fuel injection systemaccording to claim 1, wherein the fuel swirl chamber is formed so as tobe surrounded by walls of the fuel swirler, valve body and valve seat.3. A fuel injection system according to claim 1, wherein the fuel swirlchamber is formed to a circularly annular shape, the swirl groovesextending in a tangential direction of the fuel swirl chamber.
 4. A fuelinjection system according to claim 1, wherein surfaces of the fuelswirler and valve seat at which these parts contact each other areinclined with respect to the axes thereof.
 5. A fuel injection systemaccording to claim 4, wherein an angle of inclination of the contactsurfaces with respect to the mentioned axes is not smaller than 45° andsmaller than 90°.
 6. A fuel injection system according to claim 1 ,wherein the average cross-sectional area S3 is determined by using thefollowing equation: S3=(π/4){De ² −Q ² sin² ΘDi ²ρ/(2 gPA ²)} whereinDe: an inner diameter (m) of the fuel injection port, Q: a static flowrate (m³/s) of a fuel supplied to the fuel swirler, A: a totalcross-sectional area (m²) of the swirl grooves, Di: a length (m) twotimes as large as an offset amount of the center line of the swirlgrooves with respect to the center of the fuel swirl chamber, Θ: anangle (°) of surfaces of the valve seat and fuel swirler at which theseparts contact each other with respect to the axes thereof, g:gravitational acceleration (m/s²) P: pressure (kgf/m²) of the fuelsupplied to the fuel swirler, and ρ: density (kg/m³) of the fuel.
 7. Afuel injection system according to claim 1, wherein the swirl grooveshave a non-square cross-sectional shape, the volume per unit length ofeach of the swirl grooves of groove bottoms or the portions of thegrooves which are in the vicinity of the groove bottoms being smallerthan that per unit length of each of the grooves of upper portions ofthe grooves.